package com.relax.mybatis.encrypt.algorithm;

import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

import javax.crypto.Cipher;

import com.relax.mybatis.constant.EncryptConstants;

/**
 * @author hebin
 * @date 2021/03/09
 * @desc RSA编码器<br>
 *       注：所有传入及传出字符串均使用BASE64编码
 */
public class RSA {

    public static final String KEY_ALGORITHM = "RSA";

    public static final int MIN_KEY_SIZE = 512;

    public static final int MAX_KEY_SIZE = 2048;

    public static final int DEFAULT_KEY_SIZE = 1024;

    public static final String SIGNATURE_ALGORITHM = "MD5withRSA";

    private static final String PUBLIC_KEY = "RSAPublicKey";

    private static final String PRIVATE_KEY = "RSAPrivateKey";

    /**
     * 获取密钥对
     * 
     * @return
     * @throws Exception
     */
    public static Map<String, Object> getKeyMap() throws Exception {
        return getKeyMap(DEFAULT_KEY_SIZE);
    }

    /**
     * 获取密钥对
     * 
     * @param keySize
     *            密钥长度，取值范围为[512,2048]，默认1024
     * @return
     * @throws Exception
     */
    public static Map<String, Object> getKeyMap(int keySize) throws Exception {
        if (keySize < MIN_KEY_SIZE) {
            keySize = MIN_KEY_SIZE;
        }
        if (keySize > MAX_KEY_SIZE) {
            keySize = MAX_KEY_SIZE;
        }
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(KEY_ALGORITHM);
        keyPairGen.initialize(DEFAULT_KEY_SIZE);
        KeyPair keyPair = keyPairGen.generateKeyPair();
        RSAPublicKey publicKey = (RSAPublicKey)keyPair.getPublic();
        RSAPrivateKey privateKey = (RSAPrivateKey)keyPair.getPrivate();
        Map<String, Object> keyMap = new HashMap<String, Object>(2);
        keyMap.put(PUBLIC_KEY, publicKey);
        keyMap.put(PRIVATE_KEY, privateKey);
        return keyMap;
    }

    /**
     * 获取公钥
     * 
     * @param keyMap
     * @return
     * @throws Exception
     */
    public static String getPublicKey(Map<String, Object> keyMap) throws Exception {
        Key key = (Key)keyMap.get(PUBLIC_KEY);
        return Base64.encodeToString(key.getEncoded());
    }

    /**
     * 获取私钥
     * 
     * @param keyMap
     * @return
     * @throws Exception
     */
    public static String getPrivateKey(Map<String, Object> keyMap) throws Exception {
        Key key = (Key)keyMap.get(PRIVATE_KEY);
        return Base64.encodeToString(key.getEncoded());
    }

    /**
     * 用私钥对信息生成数字签名
     * 
     * @param data
     *            加密数据
     * @param privateKey
     *            私钥
     * 
     * @return
     * @throws Exception
     */
    public static String sign(String data, String privateKey) throws Exception {
        byte[] bytes = data.getBytes();
        return sign(bytes, privateKey);
    }

    /**
     * 用私钥对信息生成数字签名
     * 
     * @param data
     *            加密数据
     * @param privateKey
     *            私钥
     * 
     * @return
     * @throws Exception
     */
    public static String sign(byte[] data, String privateKey) throws Exception {
        // 解密由base64编码的私钥
        byte[] keyBytes = Base64.decode(privateKey);
        // 构造PKCS8EncodedKeySpec对象
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        // 指定加密算法
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        // 取私钥匙对象
        PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);

        // 用私钥对信息生成数字签名
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initSign(priKey);
        signature.update(data);

        return Base64.encodeToString(signature.sign());
    }

    /**
     * 校验数字签名
     * 
     * @param data
     *            加密数据
     * @param publicKey
     *            公钥
     * @param sign
     *            数字签名
     * 
     * @return 校验成功返回true 失败返回false
     * @throws Exception
     * 
     */
    public static boolean verify(String data, String publicKey, String sign) throws Exception {
        byte[] bytes = data.getBytes();
        return verify(bytes, publicKey, sign);
    }

    /**
     * 校验数字签名
     * 
     * @param data
     *            加密数据
     * @param publicKey
     *            公钥
     * @param sign
     *            数字签名
     * 
     * @return 校验成功返回true 失败返回false
     * @throws Exception
     * 
     */
    public static boolean verify(byte[] data, String publicKey, String sign) throws Exception {
        // 解密由base64编码的公钥
        byte[] keyBytes = Base64.decode(publicKey);
        // 构造X509EncodedKeySpec对象
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
        // 指定加密算法
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        // 取公钥匙对象
        PublicKey pubKey = keyFactory.generatePublic(keySpec);

        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initVerify(pubKey);
        signature.update(data);

        // 验证签名是否正常
        return signature.verify(Base64.decode(sign));
    }

    /**
     * 加密<br>
     * 用公钥加密
     * 
     * @param data
     * @param key
     * @return
     * @throws Exception
     */
    public static String encryptByPublicKey(String data, String key) throws Exception {
        return Base64.encodeToString(encryptByPublicKey(data.getBytes(EncryptConstants.DEFAULT_CHARSET), key));
    }

    /**
     * 加密<br>
     * 用公钥加密
     * 
     * @param data
     * @param key
     * @return
     * @throws Exception
     */
    public static byte[] encryptByPublicKey(byte[] data, String key) throws Exception {
        // 对公钥解密
        byte[] keyBytes = Base64.decode(key);
        // 取得公钥
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key publicKey = keyFactory.generatePublic(x509KeySpec);

        // 对数据加密
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);

        return cipher.doFinal(data);
    }

    /**
     * 加密<br>
     * 用私钥加密
     * 
     * @param data
     * @param key
     * @return
     * @throws Exception
     */
    public static byte[] encryptByPrivateKey(byte[] data, String key) throws Exception {
        // 对密钥解密
        byte[] keyBytes = Base64.decode(key);
        // 取得私钥
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key privateKey = keyFactory.generatePrivate(pkcs8KeySpec);

        // 对数据加密
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.ENCRYPT_MODE, privateKey);

        return cipher.doFinal(data);
    }

    /**
     * 解密<br>
     * 用公钥解密
     * 
     * @param data
     * @param key
     * @return
     * @throws Exception
     */
    public static byte[] decryptByPublicKey(byte[] data, String key) throws Exception {
        // 对密钥解密
        byte[] keyBytes = Base64.decode(key);
        // 取得公钥
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key publicKey = keyFactory.generatePublic(x509KeySpec);

        // 对数据解密
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.DECRYPT_MODE, publicKey);

        return cipher.doFinal(data);
    }

    /**
     * 解密<br>
     * 用私钥解密
     * 
     * @param data
     * @param key
     * @return
     * @throws Exception
     */
    public static String decryptByPrivateKey(String data, String key) throws Exception {
        return new String(decryptByPrivateKey(Base64.decode(data), key));
    }

    /**
     * 解密<br>
     * 用私钥解密
     * 
     * @param data
     * @param key
     * @return
     * @throws Exception
     */
    public static byte[] decryptByPrivateKey(byte[] data, String key) throws Exception {
        // 对密钥解密
        byte[] keyBytes = Base64.decode(key);
        // 取得私钥
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key privateKey = keyFactory.generatePrivate(pkcs8KeySpec);

        // 对数据解密
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.DECRYPT_MODE, privateKey);

        return cipher.doFinal(data);
    }

    /**
     * 解密<br>
     * 用私钥解密
     * 
     * @param data
     * @param key
     * @return
     * @throws Exception
     */
    public static String decryptHexStringByPrivateKey(String data, String key) throws Exception {
        return new String(decryptByPrivateKey(Hex.decode(data), key));
    }

    public static void main(String[] args) throws Exception {
        // RSA一对密钥分为公钥和私钥，公钥用于加密，对外开放，私钥用于解密，自己保存，不公开
        // 公钥加密、私钥解密，私钥签名、公钥验签
        Map<String, Object> keyMap = getKeyMap();
        String publicKey = getPublicKey(keyMap);
        String privateKey = getPrivateKey(keyMap);
        System.out.println("公钥：");
        System.out.println(publicKey);
        System.out.println("私钥：");
        System.out.println(privateKey);

        // 场景一：加密（防止信息泄露）
        // 1.A生成一对密钥，将公钥传递给B；
        // 2.B用公钥对合同加密，并且把密文传送给A；
        // 3.A接收到密文后，使用私钥对其解密。
        // 在该场景中，有两次数据传输过程，即便这两次传输的数据都被第三方获取，也没有风险，
        // 因为只有我方保存的私钥才能够对密文进行解密
        String password = "d41d8cd98f00b204e9800998ecf8427e";
        System.out.println("加密前：");
        System.out.println(password);
        System.out.println();
        String cipher = encryptByPublicKey(password, publicKey);
        System.out.println("加密后：");
        System.out.println(cipher);
        System.out.println();
        System.out.println("解密后：");
        System.out.println(decryptByPrivateKey(cipher, privateKey));
        System.out.println();

        // 场景二：签名（防止信息被篡改）
        // 1.A生成一对密钥，用私钥对消息加签，并且将加签的消息和消息本身一起传递给B；
        // 2.B收到消息后，再获取A的公钥进行验签，如果结果为true，证明消息是A传递的。
        String data = "我是一份合同正文！";
        String signature = sign(data, privateKey);
        System.out.println("待签名数据：");
        System.out.println(data);
        System.out.println();
        System.out.println("使用私钥对数据进行签名：");
        System.out.println(signature);
        System.out.println("使用公钥校验签名结果：");
        System.out.println(verify(data, publicKey, signature));
    }

}
